The present invention relates to a method and a device for determining measured values from a time-dependent graph. The present invention is used, in particular, in the field of packaging machines, printing presses, textile machines, and automation systems. It is also possible to use the method according to the present invention, and the device according to the present invention in systems that are controlled electrically, hydraulically, or pneumatically.
It is known from the prior art to determine measured values from a time-dependent graph by outputting—using a measuring device—a point in time at which a certain measurement took place. The actual measured value may then be determined from the time-dependent graph using a method such as an interpolation method.
As with any analog or digital method of signal processing, dead times occur when using a measuring device of this type, e.g. a sensing probe function. These dead times generally result in measurement errors and therefore reduce the accuracy of the measured result. Dead time in the sensing probe signal and dead time in the sampled values affect the determination of, e.g. position values when using a sensing probe function which is integrated in the controller.
JP 7253811 A makes known a measurement control switching circuit. This switching circuit establishes a dead time for a control signal within specified times.
There are various reasons why dead time may occur in a sensing probe signal. For instance, it is possible for delays to occur in the detection of a trigger event, and in the transmission of the sensing probe signal by various components. The first delay mentioned above occurs in the sensor itself due to the processing—which is usually digital—of the measured quantity, and due to the output drivers that amplify the signal. Within the controller, dead times are caused by a current-limiting input circuit and the optical couplers.
Dead times also result from the clocked processing of the input signal, and from the digital filtering. It is possible to approximately determine the dead times to be expected by referring to data sheets for the particular sensor that is used, and to the data sheets for the control hardware. Suitable measurement series must be carried out in order to determine the exact value for these dead times, however. The above-mentioned dead times of the above-mentioned components result in the particular events being detected too late, thereby resulting in an incorrect time stamp being used as the basis for interpolating the position value or the value to be determined, which, in turn, yields an erroneous result. Due to the dead times mentioned above, it is therefore possible for position errors to occur, in particular in the determination of positive or negative slopes of a graph.